1. Field of the Invention
The present invention relates to a control device and a control system.
Priority is claimed on Japanese Patent Application No. 2009-025133, filed Feb. 5, 2009, the contents of which are incorporated herein by reference.
2. Description of Related Art
A conventional process control system is known, which is used in an oil field or a gas field. In the conventional process control system, various field devices such as a thermometer, a pressure meter, a flow meter and a valve which are provided in a plant equipment are automatically controlled. Then, a process controller which has a network communication function is connected to a maintenance management terminal or other controller via a LAN (Local Area Network) to be able to communicate with each other. Then, the process controller is connected to a remote monitoring terminal which is located in a remote location to be able to communicate with each other via a wireless network. For example, Japanese Unexamined Patent Publication, First Publication No. 2008-199091 discloses a communication system which is used for the above-mentioned process control system.
The aforementioned process controller supplies a process data which is collected from various field devices to a maintenance management terminal and other controller via the LAN, or supplies the process data to a remote monitoring terminal via the wireless network. Therefore, a system administrator is allowed to perform reading and managing of process data, and remote operation of the process controller by the remote monitoring terminal, even if the system administrator resides in a remote location. On the other hand, a field engineer is allowed to perform reading and managing of process data and maintenance inspection operation of each device which includes the process controller, by the maintenance management terminal.
The process controller includes a network controller for performing a communication connection with the LAN (TCP/IP connection) and data transmission and reception via the LAN. Generally, the network controller is mounted on a substrate as a discrete semiconductor IC chip which is separate from a CPU (Central Processing Unit). The network controller regularly or irregularly performs communication operation (communication connection, data transmission and reception) in response to a request from the CPU or a request from the maintenance management terminal or other controller. Therefore, the network controller has a larger power consumption relative to other parts or components.
A chemical plant such as an oil field or a gas field is often constructed in a place which is poor in power supply infrastructure.
Therefore, it has been proposed to use a solar power generation to compensate power shortage. Thus, it is necessary to reduce power consumption of the process control system as a whole. Therefore, a method of reducing power consumption has been proposed to improve the network controller which has large power consumption.
For example, a network controller can be used which has a switching function to a power saving mode. In the network controller, a process controller has a manual power saving function and an automatic power saving function. The manual power saving function allows the network controller to be manually set into or reset from the power saving mode. The automatic power saving function monitors data received by the network controller so as to set the network controller into the power saving mode if any data is not received during a predetermined time period.
In case of the aforementioned manual power saving function, an external switch which is manually-operable is provided in the process controller. A power saving management function of the CPU transmits, to the network controller, instructions which switch between ON-state and OFF-state of the power saving mode in response to a switching operation of the external switch. In case of the automatic power saving function, the number of reception data of the network controller is monitored by the power saving management function. If data is not received during a monitoring time period, instructions which switch the power saving mode to the ON-state are transmitted to the network controller by the power saving management function.